| An apparatus includes a first platform and a second platform configured to rotate relative to the first platform about an axis. A magnet ring is mounted to the first platform and centered around the axis. The magnet ring includes four or more magnetized poles positioned such that each respective boundary between neighboring poles is shifted relative to a corresponding nominal boundary defined by a uniform spacing of boundaries of the poles around the magnet ring. Idle shifted boundaries of the poles define a characteristic shift pattern for the magnet ring. A magnetic field sensor is connected to the second platform. Circuitry is configured to (i) determine a magnetic field pattern generated by the poles based on data generated by the sensor and (ii) determine a rotational position of the first platform relative to the second platform by correlating the magnetic field pattern to the characteristic shift pattern. |
